avr butterfly and jtag

I have bought an AVR Butterfly as my first step in exploring the 
wonderful world of microcontrollers, and have worked out how
to compile and load programs into it using WinAVR, AVR Studio
and the RS232 connection. And all for � 30!

Now I want to try my hand at on board debugging. Do I just buy
the JTAG dongle for � 45 and talk through it to the Butterfly 
with AVR Studio? I can hardly believe it is that simple. 
Why does the JTAG ICE cost 
so much more? Am I missing something here?

Is there some issue with the fact that the dongle expects 5 volts from
the target, but the Butterfly only takes up to 4.5 volts external power?

Thanks for any advice

--

Mark

markwandrew@hotmail.com (Mark Andrew) wrote in message news:<5a9a008e.0405291141.5a3568d1@posting.google.com>...
> I have bought an AVR Butterfly as my first step in exploring the 
> wonderful world of microcontrollers, and have worked out how
> to compile and load programs into it using WinAVR, AVR Studio
> and the RS232 connection. And all for ? 30!
> 
> Now I want to try my hand at on board debugging. Do I just buy
> the JTAG dongle for ? 45 and talk through it to the Butterfly 
> with AVR Studio? 

JTag ISP dongle can only program the chip, not debugging.

I can hardly believe it is that simple. 
> Why does the JTAG ICE cost 

Jtag ICE (In Circuit Emulator) can debug the target.

> so much more? Am I missing something here?
> 
> Is there some issue with the fact that the dongle expects 5 volts from
> the target, but the Butterfly only takes up to 4.5 volts external power?

I use two diodes to drop 5V to 3.6V to power the butterfly.  The
on-board battery is 3.6V, not 4.5V.

> Thanks for any advice

me@linnix.com (Edward Lee  epl) wrote in message news:<c6a6fa27.0405291900.71a5cd3b@posting.google.com>...
> markwandrew@hotmail.com (Mark Andrew) wrote in message news:<5a9a008e.0405291141.5a3568d1@posting.google.com>...

> > Now I want to try my hand at on board debugging. Do I just buy
> > the JTAG dongle for ? 45 and talk through it to the Butterfly 
> > with AVR Studio? 
> 
> JTag ISP dongle can only program the chip, not debugging.
> 
Are we talking about the same thing? According to ...
http://www.olimex.com/dev/avr-jtag.html
... it can do everything

> I can hardly believe it is that simple. 
> > Why does the JTAG ICE cost 
> 
> Jtag ICE (In Circuit Emulator) can debug the target.
> 
> > so much more? Am I missing something here?
> >